A cable for hoisting apparatuses, made up of a twisted cable bundle incased in polyurethane (3) forming a constant circular outer section, wherein the central or inner cable (1) is thicker than the remaining cables (2) located peripherally around the former, and all of them are in turn formed by twisted pearlitic steel filaments (4-5), those filaments making up the central or inner cable (1) being of a larger section than those forming the peripheral cables (2).
As indicated by the title, the present invention refers to a cable for elevators and hoists which are joined to the passenger car at one end and to a counterweight at the other end, passing through an upper drive pulley.
Elevator or hoist cables are usually made up of a central steel or natural organic fiber core around which a series of cable bundles, usually of steel also, are arranged. A mixed solution with a central core separated from surrounding bundles by an insulating layer is represented in patent document EP 0 444 245.
Patent document EP 0 633 350 discloses a cable formed by a central core with a series of steel cable bundles, which is surrounded by a series of cable bundles, the outer filaments of which are metal and surround a central core of greater diameter, formed by a synthetic material, such as polyethylene, polypropylene, polyamide or other similar substances.
Patent document ES 2 141 851 discloses a cable comprising a central cable bundle, surrounded by a sheath, around which a second group of cables is arranged, also externally protected by another synthetic sheath. In both cases, in the inner and outer layer, the cables are of aramide and the sheath of the inner cables is of polyester, plastic or silicone, whereas the outer sheath layer is of polyurethane.
Patent document DE 1 904 468 refers to a process for manufacturing a wire cable with a synthetic material sheath protecting the cable from moisture, and accordingly from oxidation; wires of synthetic material that are melted and fused to the final sheath are inserted among the metal cables, thus perfectly incasing the inner metal cables.
Given that a failure in cables from which the passenger car of the elevator hangs could have terrible consequences for the people who use it, the safety factors required of elevator and hoist cables are very high. In Spain, elevator cables must be of steel and the ratio between the diameter of the pulleys and the diameter of the cables must be at least 40. The reason for these large pulleys is to minimize fatigue and wear of the steel cables in their continuous swaying on the pulleys.
However, if an elevator machinery occupying lesser volume, particularly in height, is desired, it is necessary to reduce the diameter of the pulleys, and accordingly the diameter of the cable bearing the passenger car; to do this, the use of pearlitic steel filament cables similar to those used in the reinforcement of automotive tires is resorted to, having a very small diameter and being particularly flexible and fatigue resistant with alternating loads.
The solution proposed in the present invention consists of a cable having a twisted cable bundle, wherein a central or inner cable is thicker than those located peripherally around the former. Each one of these cables is in turn formed by a constant number of twisted pearlitic steel filaments, the filaments making up the central or inner cable having a greater section. The strand thus formed is incased in polyurethane, forming a constant circular section.
These filament bundles forming each one of the components of the main cable are very thin and therefore flexible pearlitic steel filaments of high mechanical resistance.
According to an important feature of the present invention, the twist direction of the main cable bundle is opposite to the twist direction of the filaments making up each one of these cables.
The cable bundle it forms is made up of an inner cable and six cables twisted around this central cable, and the twist pitch of this bundle is comprised between 25 and 55 mm.
Both the central cable and the cables twisted around it are formed by an identical number of pearlitic steel filaments, comprised between 15 and 25.
With the mentioned specifications and adjusting the twist pitch of the filaments of the central cable or strand and of the filaments of the outer cables or strands, while at the same time also adjusting the twist pitch of the outer cables on the central cable and carrying out the twisting of the central cable with respect to the peripheral cables in opposite directions, the diameter of the section of a standard cable of this type is reduced, sheathed with a material that is between 35 and 40% synthetic, maintaining, however, the breaking load adjusted to the standards for hoisting apparatuses.
The object of the invention will be better understood with the aid of the following description made based on a practical embodiment; this description is made based on the attached drawings, wherein:
The cable for hoisting apparatuses object of the invention is made up of a twisted cable bundle (1-2) incased in polyurethane (3) forming a constant circular outer section. The central or inner cable (1) is thicker than the remaining cables (2) located peripherally around the former, and as can be observed in the figures, the inner cable (1) is surrounded by six twisted cables (2), all of them with a twist pitch (P) comprised between 25 and 55 mm, preferably 50 mm.
Each one of the main cables (1-2) is in turn formed by a constant number of twisted pearlitic steel filaments (4-5), those making up the central or inner cable (1) being of a larger section than those making up the peripheral cables (2). The number of filaments of each one of these cables (1-2) is comprised between 15 and 25, preferably 19, and the twist pitch (p) of the filaments (4-5) upon forming the cables (1-2) is comprised between 25 and 55 mm, preferably 50 mm.
As can be observed in Figure 2, the twist direction of the main cable bundle (1-2) is opposite to the twist direction of the filaments (4-5) making up each one of these cables.
The cable bundle (1-2) is incased in polyurethane forming a sheath (3) of circular section having an outer surface (3a) over the outer cables (2).
It is not considered necessary to extend this description so that a person skilled in the art may understand the scope of the invention and the advantages derived therefrom.
The materials, shape and arrangement of the elements will be susceptible of variation provided that this implies no alteration of the essential features of the invention, which are claimed below.